refrigeration and hvac - festo

Refrigeration and HVAC

Geothermal Heat Pump Systems

With a regulated temperature of the simulated ground

Job Sheets - Courseware Sample 89952-F0

Order no.: 89952-30 First Edition Revision level: 04/2015

By the staff of Festo Didactic

© Festo Didactic Ltée/Ltd, Quebec, Canada 2013 Internet: www.festo-didactic.com e-mail: [email protected]

Printed in Canada All rights reserved ISBN 978-2-89640-839-9 (Printed version) ISBN 978-2-89640-840-5 (CD-ROM) Legal Deposit – Bibliothèque et Archives nationales du Québec, 2013 Legal Deposit – Library and Archives Canada, 2013

The purchaser shall receive a single right of use which is non-exclusive, non-time-limited and limited geographically to use at the purchaser's site/location as follows.

The purchaser shall be entitled to use the work to train his/her staff at the purchaser's site/location and shall also be entitled to use parts of the copyright material as the basis for the production of his/her own training documentation for the training of his/her staff at the purchaser's site/location with acknowledgement of source and to make copies for this purpose. In the case of schools/technical colleges, training centers, and universities, the right of use shall also include use by school and college students and trainees at the purchaser's site/location for teaching purposes.

The right of use shall in all cases exclude the right to publish the copyright material or to make this available for use on intranet, Internet and LMS platforms and databases such as Moodle, which allow access by a wide variety of users, including those outside of the purchaser's site/location.

Entitlement to other rights relating to reproductions, copies, adaptations, translations, microfilming and transfer to and storage and processing in electronic systems, no matter whether in whole or in part, shall require the prior consent of Festo Didactic GmbH & Co. KG.

Information in this document is subject to change without notice and does not represent a commitment on the part of Festo Didactic. The Festo materials described in this document are furnished under a license agreement or a nondisclosure agreement.

Festo Didactic recognizes product names as trademarks or registered trademarks of their respective holders.

All other trademarks are the property of their respective owners. Other trademarks and trade names may be used in this document to refer to either the entity claiming the marks and names or their products. Festo Didactic disclaims any proprietary interest in trademarks and trade names other than its own.

© Festo Didactic 89952-30 III

Safety and Common Symbols

The following safety and common symbols may be used in this manual and on the equipment:

Symbol Description

DANGER indicates a hazard with a high level of risk which, if not avoided, will result in death or serious injury.

WARNING indicates a hazard with a medium level of risk which, if not avoided, could result in death or serious injury.

CAUTION indicates a hazard with a low level of risk which, if not avoided, could result in minor or moderate injury.

CAUTION used without the Caution, risk of danger sign , indicates a hazard with a potentially hazardous situation which, if not avoided, may result in property damage.

Caution, risk of electric shock

Caution, hot surface

Caution, risk of danger

Caution, lifting hazard

Caution, hand entanglement hazard

Notice, non-ionizing radiation

Direct current

Alternating current

Both direct and alternating current

Three-phase alternating current

Safety and Common Symbols

IV © Festo Didactic 89952-30

Symbol Description

Earth (ground) terminal

Protective conductor terminal

Frame or chassis terminal

Equipotentiality

On (supply)

Off (supply)

Equipment protected throughout by double insulation or reinforced insulation

In position of a bi-stable push control

Out position of a bi-stable push control

© Festo Didactic 89952-30 V

Table of Contents

Preface ................................................................................................................. VII

About This Manual ................................................................................................ IX

To the Instructor .................................................................................................... XI

Job Sheet 1 Geothermal Energy .................................................................. 1

Job Sheet 2 The Ground Loop ................................................................... 33

Job Sheet 3 Heat Pump Connections and Interior Piping ...................... 59

Job Sheet 4 The Refrigeration Cycle ........................................................ 91

Job Sheet 5 Psychrometrics .................................................................... 121

Job Sheet 6 Geothermal Heat Pumps ..................................................... 149

Job Sheet 7 Heat Exchangers .................................................................. 169

Job Sheet 8 Heat Pump Control and Safety Devices ............................ 197

Job Sheet 9 System Characterization ..................................................... 247

Job Sheet 10 Maintenance and Troubleshooting .................................... 257

Job Sheet 11 Geothermal Software Design Tools ................................... 269

Appendix A Conversion Table ................................................................. 289

Appendix B Pressure-Enthalpy Diagrams .............................................. 291

Appendix C Psychrometric Charts ......................................................... 293

Appendix D Anemometer Instructions ................................................... 295

Appendix E Thermo-Fusion Joints on Geothermal Pipes .................... 299

Appendix F Priming Procedures ............................................................. 307

Table of Contents

VI © Festo Didactic 89952-30

Appendix G Maintenance and Water Conditioning ............................... 309

Index................................................................................................................... 311

© Festo Didactic 89952-30 VII

Preface

Geothermal heat pump systems, also known as ground source heat pumps, are among the most energy efficient systems available today for HVAC applications. Depending on geographical location, typical energy savings from a geothermal heat pump system are from 25% to 70%.

The Geothermal Training System, Model 46126, allows you to develop knowledge in heat transfer, refrigeration, and air conditioning. The topics covered in the job sheets are designed to help you gain the skills required during installation, operation, and troubleshooting of geothermal heat pump systems.

The tools and instruments commonly used with geothermal heat pump systems are also introduced and, when applicable, are used during hands-on activities.

We invite readers of this manual to send us their tips, feedback, and suggestions for improving the book.

Please send these to [email protected].

The authors and Festo Didactic look forward to your comments.

© Festo Didactic 89952-30 IX

About This Manual

Description

The topics covered in this manual are presented in the form of job sheets. Each job sheet consists of a theoretical section named Information Job Sheet followed by a series of tasks required to attain the learning objectives.

This manual is to be used with the Geothermal Training System equipped with two heat pumps (46126-A). The second heat pump is used to maintain the simulated ground at an almost constant temperature.

Safety considerations

Safety symbols that may be used in this manual and on the equipment are listed in the Safety Symbols table at the beginning of the manual.

Safety procedures related to the tasks that you will be asked to perform are indicated in each exercise.

Make sure that you are wearing appropriate protective equipment when performing the tasks. You should never perform a task if you have any reason to think that a manipulation could be dangerous for you or your teammates.

System of Units

Units are expressed using the International System of Units (SI) followed by the units expressed in the U.S. customary system of units (between parentheses).

Most of the components of the geothermal training system are machined using the US customary system of units. The job sheet calculations have been done using both the SI and US customary systems of units. The results in US customary units are shown in parentheses to the right of the SI values.

Appendices

The appendices included in this manual are:

Appendix A - Conversion Table: Factors to apply to convert US customary units to SI units and vice versa.

Appendix B - Pressure-Enthalpy Diagrams: Pressure-enthalpy diagrams of the refrigerant used in the training system.

Appendix C - Psychrometric Charts: Standard air psychrometric charts.

Appendix D - Anemometer Instructions: Operating instructions of the anemometer supplied with the training system.

About This Manual

X © Festo Didactic 89952-30

Appendix E - Thermo-Fusion Joints on Geothermal Pipes: Explains how to make joints on geothermal pipes.

© Festo Didactic 89952-30 XI

To the Instructor

You will find in this Instructor Guide all the elements included in the Student Manual together with the answers to all questions, results of measurements, graphs, explanations, suggestions, and, in some cases, instructions to help you guide the students through their learning process. All the information that applies to you is placed between markers and appears in red.

Accuracy of measurements

The numerical results of the hands-on exercises may differ from one student to another. For this reason, the results and answers given in this manual should be considered as a guide. Students who correctly performed the exercises should expect to demonstrate the principles involved and make observations and measurements similar to those given as answers.

Sample Extracted from

the Job Sheets Student and the Job Sheets Instructor

© Festo Didactic 89952-30 169

Heat pumps

Introduction

Heat exchangers are devices that transfer energy from a warmer fluid to a colder one. The role of the exchanger is to optimize the transfer of heat by providing a space where the two fluids interact thermally as much as possible. The fluids do not mix together during the heat exchange process due to a physical barrier between them. The exchanger provides a surface area that allows the heat of the hot fluid to be transferred by conduction to the cold fluid through the thin, heat-conductive walls separating the fluids.

There are different devices that exchange heat that are not strictly considered heat exchangers. In general, devices that mix two fluids at different temperatures are considered mass and heat exchangers. Mixing chambers, such as a kitchen faucet that mixes hot and cold water together, are a good example of such devices. However, we will not discuss such exchangers in this manual.

The heat that is exchanged in a given fluid can be expressed by the following equation:

(7-1)

where is the heat flow of the fluid in W (Btu/h)

is the mass flow rate of the fluid in kg/s (lbs/h)

is the constant pressure specific heat of the fluid (e.g., 4190 J/kg °C (1.00 Btu/lb °F) for water at room temperature) in J/kg·K (Btu/lb·°F)

is the temperature of the fluid entering the heat exchanger in °C (°F)

is the temperature of the fluid leaving the heat exchanger in °C (°F)

a The fluids in a heat exchanger could be identified by a sub-index such as: "r" for the refrigerant, "w" for water, "h" for the hot fluid, and "c" the cold fluid. The equation for the hot fluid in an exchanger would then become:

.

Configurations of heat exchangers are available for different applications. One of the most common types of exchanger is the coaxial type shown in the bottom of Figure 106. In this exchanger, the fluids travel on the same axis on parallel trajectories. The coaxial type exchanger is used on your training system. Both the desuperheater and the geothermal heat pump ground-loop water/refrigerant heat exchanger are instances of coaxial exchangers.

Heat Exchangers

Information Job Sheet 7

Job Sheet 7 – Heat Exchangers

170 © Festo Didactic 89952-30

Another type of heat exchanger is called the cross-flow heat exchanger. In this arrangement, instead of traveling in the same direction, both fluids meet at a ninety degree angle. The air/refrigerant heat exchanger found at the air intake of the heat pump is an example of a cross-flow exchanger.

Heat exchanger analysis

A heat exchanger analysis allows us to determine the amount of heat that is transferred from one fluid to another. A thorough analysis also permits us to determine the temperatures at the inlet and outlet of the fluids under certain conditions.

In a coaxial heat exchanger, fluids exchange heat using one of two flow configurations: the parallel-flow configuration (Figure 106a), where hot and cold fluids enter on the same side of the exchanger, and the counter-flow configuration (Figure 106b), where the fluids enter at opposite sides of the exchanger.

The fluids continue to exchange heat as long as there is a temperature difference between the fluids at a given position in the exchanger.

Figure 106. Heat exchanger flow.

Figure 106 shows that, when the flows are parallel, the temperatures of the hot and cold fluids merge until they either reach the same temperature or they exit the exchanger. When the fluids are flowing in a counter-flow configuration, the temperature lines have a tendency to "follow each other". Note that in the counter-flow configuration, the output temperature of the hot fluid can be colder than the output temperature of the cold water as shown in Figure 106b.

Several different heat exchangers play major roles in the geothermal heat pump HVAC installations.

Position

Hot fluid

Cold fluid

Hot fluid

Cold fluid

Position

Tem

pera

ture

Tem

pera

ture

(a) (b)



The ground loop is a heat exchanger that transfers heat between the thermal fluid and the ground.

The coaxial heat exchanger in the heat pump exchanges heat between the ground loop and the refrigerant.

o When the heat pump is set to work in heating mode, this exchanger works as an evaporator. The refrigerant evaporates as it takes the energy from the ground.

o When the heat pump is working in cooling mode, the heat exchanger works as a condenser. As the refrigerant transfers heat to the ground, it is cooled and condensed into a liquid during the process.

Figure 107. Coaxial heat exchanger.

The desuperheater heat exchanger is a counter-flow heat exchanger. It exchanges heat from the refrigerant as it exits the compressor to the water in a domestic hot water (DHW) tank.

The heat pump forced-air coil exchanges heat to warm the air when heating is needed. It can also cool and dehumidify the air when air conditioning is needed. In this case, the heat extraction cools the air and condensates the water. The air cooling and the water condensation have to be taken into account if an energy balance is performed.

The heat exchangers in a heat pump may work in counter-flow or parallel-flow mode, depending on the mode of operation (heating or cooling mode).

The evaporator and condenser coils

When a change in matter occurs inside a heat exchanger, latent heat is transferred. As long as only latent heat is exchanged, the fluid that condensates or evaporates stays at the same temperature from the inlet to the outlet.

Refrigerant

Water

Refrigerant

Water



Figure 108. Condensation.

As shown in Figure 108, when condensation occurs in a heat exchanger, the temperature of the condensing fluid remains constant; but its state changes from vapor to liquid as it loses latent heat. The other fluid involved in the heat exchange gains sensible heat and its temperature rises. The state of the second fluid remains the same unless it reaches a state-change temperature (e.g., its boiling point).

When a fluid condensates on one side of the heat exchanger, the fluid on the other side absorbs heat and increases its temperature.

Figure 109. Condensation.

On the other hand, when a fluid is boiling on one side of the evaporator, the fluid on the other side cools down and releases energy.

Vapor in at T1

Liquid out at T1

Liquid in at T3

Liquid out at T2

T3<T2<T1

T

Position

Condensing refrigerant

Fluid absorbing heat

Heat flow



Figure 110. Vaporization.

In a typical heat pump, one of the flowing fluids is a refrigerant while the other fluid is either simple water or a water/antifreeze solution. Heat exchangers may work in parallel-flow or counter-flow and as either evaporators or condensers. This versatility of the heat exchanger is possible by using different valves to control the fluid flows. However, it makes this kind of heat exchangers more difficult to understand and the calculations are slightly less tractable.

The heat flow entering (evaporation) or leaving (condensation) the fluid undergoing a change of state is expressed by the equation:

(7-2)

a The and indices in the variable refer to fluid and gas respectively. This indicates that the enthalpy refers to the vaporization/condensation.

In a typical installation, the analysis of Equation (7-1) and Equation (7-2) must be combined to reflect the multiple mechanisms at work in a geothermal heat exchanger.

The effectiveness of a heat exchanger

The effectiveness of a heat exchanger can be calculated as:

(7-3)

where is the effectiveness, a dimensional number such that

is the heat flow taking place in the exchanger in W (Btu/h) is the maximum heat transfer possible for the fluid parameters in

W (Btu/h)

where is the heat flow in W (Btu/h) is the mass flow rate of the fluid in kg/s (lb/h) is the enthalpy of vaporization or condensation in

J/kg (Btu/lb)

Hot fluid releasing heat

Vaporizing refrigerant

Heat flow

T

Position



The maximum amount of heat transfer occurs when the temperature of the hot fluid drops to the temperature of the cold fluid at its inlet, or when the cold fluid reaches the temperature of the hot fluid at its inlet.

To compare the amount of heat each fluid is handling, we need to calculate the heat capacity of each fluid.

(7-4)

where is the cold fluid heat capacity rate in W/°C (Btu/h·°F) is the mass flow rate of the cold fluid in kg/s (lb/h) is the cold fluid specific heat in J/kg·°C (Btu/lb·°F)

(7-5)

where is the hot fluid heat capacity rate in W/°C (Btu/h·°F) is the mass flow rate of the hot fluid in kg/s (lb/h) is the hot fluid specific heat in J/kg·°C (Btu/lb·°F)

Keep the smallest value between and ( ) and replace it in the following equation to obtain the maximum heat transfer:

(7-6)

where is the maximum heat transfer possible in W (Btu/h) is the minimum specific heat from the fluids in W/°C (Btu/h·°F) is the temperature of the hot fluid entering the heat exchanger

in °C (°F) is the temperature of the cold fluid entering the heat exchanger

in °C (°F)

The desuperheater

The desuperheater is a heat exchanger that extracts the sensible superheat stored in the refrigerant after the compression process. In the geothermal heat pump, the desuperheater is used to warm the water in a domestic hot water tank (DHW). This "free" energy saves part of the electric work that would otherwise be required to rise the water temperature in the tank.

The energy transferred to the water by the desuperheater is shown as a blue segment in Figure 111.

Formally, in SI units, the would be expressed in units of J/kg K, where K is the Kelvin temperature unit. This would imply the use of temperatures in K instead of °C in the equations in this page. However, tempera-tures differences in °C and K are the same, making this distinction irrelevant to our needs.

T [K] = T [°C] + 273.15



Figure 111. Desuperheater graph.

A double-tube heat exchanger is installed between the compressor exit and the four-way valve to transfer the superheat to the domestic hot water tank.

The goal of this heat exchanger is to cool down the superheated refrigerant as it exits the compressor to a temperature that is only slightly above the saturation temperature.

Figure 112. Desuperheater.

The pump that circulates the water through the desuperheater should work only when the temperature of the water in the tank is lower than the saturation temperature. The refrigerant should transfer heat to the water, but the water should never transfer heat to the refrigerant. If heat is transferred to the refrigerant, the pressure increases at the compressor exit, making the system less efficient.

In heating mode, the desuperheater circulation pump is usually turned off allowing all the available heat to warm the house.

Thermal efficiency

The ratio between the heat output and the heat input of any device is the theoretical thermal efficiency.

P (abs)

Superheat recovered by the desuperheater

Refrigerant in

Water out

Refrigerant out

Water in

High pressure

Low pressure



(7-7)

From the first law of thermodynamics, the energy output of a closed system cannot exceed its input. Consequently, the thermal efficiency is always in the range between:

When expressed as a percentage, the thermal efficiency must be between 0% and 100%. Due to inefficiencies, such as friction, heat loss, and other factors, the efficiency of any real-world thermal engine is typically much less than 100%.


In this job sheet, you will determine the refrigerant mass flow rate circulating in the heat pump. You will also calibrate the water flow in the desuperheater to heat water in the domestic hot water tank (DHW) using the sensible heat from the hot, superheated refrigerant. You will determine the amount of money that could be saved with the use of a desuperheater.

1. Perform the following settings on your training system. Main power switch ............................................................................. On

Thermostat ......................................................................................... Off

Valve HV-1 ...................................................................................... Open

Valve HV-2 ...................................................................................... Open

Valve HV-3 ...................................................................................... Open

Valve HV-4 ...................................................................................... Open

Valve HV-5 ...................................................................................... Open

Valve HV-6 ...................................................................................... Open

Valve HV-7 ...................................................................................... Open

Valve HV-8 ................................................................................... Closed

Valve HV-9 ........................................................ No adjustments required

Valve HV-10 ................................................ Handle in horizontal position

Valve HV-11 .................................................................................... Open

Valve HV-12 .................................................................................... Open

Valve HV-13 .................................................................................... Open

Pressure gauge PI-1 selector switch ............................................... Right


Desuperheater On/Off switch ............................................................ On

Priming tank three-way valves ......................................................

Pumping station three-way valves .................................................

Air distribution register .................................................................... Open

Perform the following settings on the simulated ground heat pump:

Main power switch (simulated ground heat pump) ............................. On

Temperature controller set point .... 3°C (5°F) below ground temperature

Wait for the compressor of the simulated ground heat pump to start and then wait about 5 min for the temperature of the water in the tank to get close to its set point.

Heat Exchangers

Job Sheet 7

OBJECTIVES

PROCEDURE



2. Next, perform the following settings on the heat pump:

Thermostat ........................................................................ Heating mode

Temperature set point .......................5°C (9°F) above room temperature

3. Turn the valve HV-10 to the vertical position.

4. When the desuperheater indicator light turns on, adjust valve HV-9 to obtain a flow (FI-4) of 2 L/min (0.6 gal/min).

5. Locate the desuperheater heat exchanger on your training system. Complete Table 29 using the following labels: Refrigerant out, Water in, Water out, and Desuperheater pump.

Figure 113. Desuperheater.

Table 29. Desuperheater element identification.

Location Name A

B

C Refrigerant in

D

E

a The domestic hot water tank of your training system has a capacity of 9.5 L (2.5 gal).

D

E

C

B A



Table 29. Desuperheater element identification.

Location Name

A Refrigerant out

B Water in

C Refrigerant in

D Desuperheater pump

E Water out

6. What type of configuration (parallel-flow or counter-flow) is used for the heat exchanger of the desuperheater?

The heat exchanger of the desuperheater uses the counter-flow configuration.

7. Turn valve HV-10 to the horizontal position.



8. Measure the temperatures and pressures shown in Table 30. Wait for fifteen minutes and repeat your measurements. Complete Table 30.

Table 30. Domestic hot water data.

LP

HP

Table 30. DHW data (SI units).

(°C) 8.5 3.4 (°C) 67.4 69.7 (°C) 42.1 46.9 (°C) 32.9 31.1 (°C) 21.4 36.5 (°C) 26.5 39.4

LP (bar) 8.3 7.0 HP (bar) 24.0 24.0

Table 30. DHW data (US customary units).

(°F) 47 40 (°F) 130 153 (°F) 109 111.6 (°F) 95.8 89.3 (°F) 68.6 89.7 (°F) 87.7 95.9

LP (psia) 125 110 HP (psia) 350 375



9. Using a pressure-enthalpy diagram included at the end of this job sheet, find the saturation temperature for the value of HP found after fifteen minutes (remember that HP is a gauge pressure).

Saturation temperature : _______

Saturation temperature (T_sat): 40°C (115°F)

10. Turn valve HV-10 to the vertical position and let the water run for one minute. Turn valve HV-10 to the horizontal position and measure TC-10.

Temperature measured by TC-10: _______

Temperature measured at TC-10: 46.9°C (111.6°F) The temperature must be adjusted to 42°C (119°F) for the operating conditions of the system given in this example. Results may vary.

11. Next, adjust valve HV-9 to obtain a temperature measured by TC-10 that is 2°C (4°F) over the saturation temperature found in step 0.

Set the thermostat operating mode to Off.

12. Calculate the energy gained by the water from to using Equation (7-8) and the temperatures measured at TC-15:

(7-8)

where is the heat gained by the water in J (Btu) is the mass of water in kg (lb)

A 9.5 liter (2.5 gallon) water heater corresponds to 9.5 kg (20.875 lb) of water.

is the constant pressure specific heat of water in J/kg·°C (Btu/lb·°F)

is the temperature of the water after fifteen minutes of running the system in °C (°F)

is the temperature of water at the beginning of the experiment in °C (°F)

SI units

= 9.5 × 4.18 × (36.5 - 21.4) = 599.6 kJ

US customary units

= 20.875 × 1.0 × (89.7 - 68.6) = 440.5 Btu



13. The heat flow rate of the process corresponds to the total heat gained by the water in the tank (calculated in step 12) divided by the number of seconds in fifteen minutes or 0.25 hours.

(7-9)

where is the heat flow rate in W (Btu/h) is the total heat gained by water in J (Btu) is the time elapsed in seconds (SI units) or hours (US units)

Calculate the heat flow rate of the process:

SI units

Heat flow rate of the process =

US customary units Heat flow of the process = 1762 Btu/h

14. Plot the compression cycle in a pressure-enthalpy diagram (Figure 118 or Figure 119) and fill in Table 31.

Table 31. Temperature-enthalpy.

Enthalpy TC–915 min

TC–1015 min



The compression cycle is given in the graph below.

Compression cycle.

Table 31. Temperature-enthalpy (SI units).

Enthalpy (kJ/kg)

TC – 915 min 470

TC – 1015 min 438

Table 31. Temperature-enthalpy (US customary units).

Enthalpy (Btu/lb)

TC – 915 min 136

TC – 1015 min 123

P (abs)

TC-10

Low pressure

TC-9TC-11High pressure

TC-8



15. Locate the TC-10 point on the pressure-enthalpy diagram. Is the desuperheater working in its ideal range of operation? Why?

No. To be in its ideal range, the desuperheater should operate in such a way that the TC-10 point is located precisely on the boundary of sensible enthalpy for the gaseous state. The actual position of TC-10 is slightly to the right of the boundary.

16. What would be the effect on the temperature read by TC-10 if you were to modify the desuperheater flow rate?

Increasing the flow rate into the desuperheater would move the TC-10 point to the left, eventually past the boundary and into the latent enthalpy region of the cycle. Decreasing the flow rate would move the TC-10 point to the right, leaving more heat available to heat the room.

17. Explain why it is preferable that the temperature at TC-10 does not drop below the saturation temperature?

If TC-10 drops below the saturation pressure, too much heat is transferred to the DHW. This does not have much impact if the system is in cooling mode. However, in heating mode, the system may simply be unable to heat the house as needed.

18. To calculate the refrigerant mass flow that circulates, compare the heat flow absorbed by the water with the enthalpy difference corresponding to the temperatures and .

(7-10)

where is the water heat flow in W (Btu/h) measured in step 13 is the refrigerant mass flow rate in kg/s (lbs/h) is the enthalpy corresponding to TC-10 in J/kg (Btu/lb) is the enthalpy corresponding to TC-9 in J/kg (Btu/lb)

SI units

kg/s

US customary units

lb/hour



19. Calculate the amount of money the desuperheater saves in heating costs for one hour of continuous work. Assume one kWh costs $0.08 (U.S.). b Electric work (We

SI units

kW

Savings = 0.053 $ per hour

US customary units

Btu/h = 1762 Btu/h ÷ 3.413 Btu/h W = 0.516 kW Savings = 0.041 $ per hour



Coaxial coil heat exchanger

The following exercise is optional and explores the characteristics of the heat pump coaxial heat exchanger. You will calculate the refrigerant mass flow using the coaxial heat exchanger in heating mode and in cooling mode. You will also determine how the heat exchanger works in each mode.

20. Perform the following adjustments to the settings of your training system. Leave the simulated ground heat pump running.

Main power switch .............................................................................. On

Thermostat ........................................................................ Heating mode

Temperature set point ....................... 5°C (9°F) above room temperature

Valve HV-1 ..................................................................................... Open

Valve HV-2 ..................................................................................... Open

Valve HV-3 ..................................................................................... Open

Valve HV-4 ..................................................................................... Open

Valve HV-5 ..................................................................................... Open

Valve HV-6 ..................................................................................... Open

Valve HV-7 ..................................................................................... Open

Valve HV-8 ................................................................................... Closed

Valve HV-9 ....................................................... No adjustments required


Valve HV-11 ................................................................................... Open

Valve HV-12 ................................................................................... Open

Valve HV-13 ................................................................................... Open



Desuperheater On/Off switch ............................................................ Off

Priming tank three-way valves .......................................................





21. Allow your training system to run for ten minutes. Complete Table 32.

Table 32. Temperature, pressure, and flow in heating mode.

LP

Ground loop water flow

Table 32. Temperature, pressure, and flow in heating mode (SI units).

(°C) 16

(°C) 14.2

(°C) 22.1

(°C) 18.4

LP (bar) 10.6

Ground loop water flow (L/min) 11

Table 32. Temperature, pressure, and flow in heating mode (US customary units).

(°F) 60.8

(°F) 57.6

(°F) 71.8

(°F) 65.1

LP (psi) 154

Ground loop water flow (gal/min) 2.9

22. Fill in the blanks with your temperature readings and draw arrows to show the fluid flow in Figure 114.

Figure 114. Heating mode heat exchanger analysis.

T=

T=

T= T=



Figure 114. Heating mode heat exchange analysis.

23. Plot a simple graph to show how the temperature of each fluid varies as they flow through the system (as shown in Figure 110).

Figure 115. Heat exchanger temperature tendency in heating mode.

Position

Tem

pera

ture

TC-8, TC-13 TC-12, TC-14

T = 14.2 T = 16°C

T = 22 T = 18



The evolution of the temperature looks like this in the exchanger

Figure 115. Heat exchanger temperature tendency in heating mode.

24. In heating mode, does the heat exchanger work in parallel-flow or counter-flow mode?

The heat exchanger works in counter-flow mode.

25. Is the heat exchanger working as an evaporator or a condenser?

The heat exchanger works as an evaporator.

100.8 Position

Tem

pera

ture

TC-8, TC-13 TC-12, TC-14

Water out

Refrigerant in

Water in

Refrigerant out



26. Perform the following adjustments to your training system. Leave the simulated ground heat pump running.

Main power switch .............................................................................. On

Thermostat ........................................................................ Cooling mode

Temperature set point ....................... 5°C (9°F) below room temperature

Valve HV-1 ..................................................................................... Open

Valve HV-2 ..................................................................................... Open

Valve HV-3 ..................................................................................... Open

Valve HV-4 ..................................................................................... Open

Valve HV-5 ..................................................................................... Open

Valve HV-6 ..................................................................................... Open

Valve HV-7 ..................................................................................... Open

Valve HV-8 ................................................................................... Closed

Valve HV-9 ....................................................... No adjustments required


Valve HV-11 ................................................................................... Open

Valve HV-12 ................................................................................... Open

Valve HV-13 ................................................................................... Open



Desuperheater On/Off switch ............................................................ Off

Priming tank three-way valves .......................................................





27. Allow your training system to run for ten minutes. Complete Table 33.

Table 33. Temperature, pressure, and flow in cooling mode.

HP

Ground loop water flow

Table 33. Cooling mode (SI units).

(°C) 35.2

(°C) 32.9

(°C) 28.6

(°C) 32.2

HP (bar) 20

Ground loop water flow (L/min) 11

Table 33. Cooling mode (US customary units).

(°F) 95.4

(°F) 91.2

(°F) 83.5

(°F) 90.0

HP (psi) 290

Ground loop water flow (gal/min) 2.9



28. Set the thermostat operating mode to Off, then shut down your training system by setting both main power switches to Off.

29. Complete the next figure by filling the measured temperatures in the blanks and draw arrows to show the fluid flows.

Figure 116. Cooling mode heat exchange analysis.

Figure 116. Cooling mode heat exchange analysis.

T=

T=

T=

T=

T = 32.9

T = 32.2

T = 35.2

T = 28.6



30. Plot a simple graph to show the drop in temperature as the fluid progresses in the heat exchanger (Use Figure 109 as a reference).

Figure 117. Heat exchanger temperature tendency in cooling mode.

The evolution of the temperature looks like this in the exchanger:

Figure 117. Heat exchanger temperature tendency in cooling mode.

31. In cooling mode, does the heat exchanger work in parallel-flow or counter-flow mode?

The heat exchanger works in parallel-flow mode.

280.8

Tem

pera

ture

PositionTC-10, TC-13 TC-12, TC-14

Position

Tem

pera

ture

TC-10, TC-13 TC-12, TC-14

Water out

Refrigerant in

Water in

Refrigerant out



Figure 118. Pressure enthalpy diagram, SI units.



Figure 119. Pressure enthalpy diagram, English units.

Name: ______________________________ Date: ____________________

Instructor's approval: _______________________________________________

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